The present invention relates in general to a display control technology and in particular to a technology well applicable to the liquid-crystal driving method such as a technology effectively usable in a display control circuit of a liquid-crystal driving apparatus for displaying dot-matrix characters.
The conventional liquid-crystal driving apparatus for displaying dot-matrix characters comprises a display RAM unit, referred to hereafter as a DDRAM unit, for storing character codes and character-generator RAM and ROM units, referred to hereafter as CGRAM and CGROM units respectively, for storing character font patterns. A CPU (Central Processing Unit) writes codes of characters for display use into DDRAM addresses which correspond to positions on a liquid-display screen. The CPU also writes any arbitrary font patterns into the CGRAM unit. An operation to control liquid-crystal display is carried out as follows. First of all, a liquid-crystal display controller reads out the code of a character stored in the DDRAM unit at an address corresponding to a display position. The code of a character read out from the DDRAM unit is then used as part of an address of the CGRAM or CGROM unit from which a character font pattern is finally read out for display. Accordingly, in order to display a picture pattern other than the dot-matrix characters such a mark or an icon, it is necessary in the case of this configuration to use part of the CGRAM or CGROM unit for dedicatedly storing picture patterns such as marks and icons. An example of a liquid-crystal driving apparatus, that incorporates CGRAM and CGROM units, is the LCD-II made by Hitachi, Ltd. For details of the LCD-II, refer to the HD44780 on Pages 1 to 12 of the user's manual which was published in February 1984.